Cable television networks such as those provided by Comcast Cable Communications, Inc., of Philadelphia, Pa., Cox Communications of Atlanta, Ga., Tele-Communications, Inc., of Englewood, Colo., Time-Warner Cable, of Marietta, Ga., Continental Cablevision, Inc., of Boston, Mass., and others provide cable television services to a large number of subscribers over a large geographical area. The cable television networks typically are interconnected by cables such as coaxial cables or a Hybrid Fiber/Coaxial ("HFC") cable system which have data rates of about 10 Mega-bits-per-second ("Mbps") to 30+ Mbps.
The Internet, a world-wide-network of interconnected computers, provides multi-media content including audio, video, graphics and text that typically requires a large bandwidth for downloading and viewing. Most Internet Service Providers ("ISPs") allow customers to connect to the Internet via a serial telephone line from a Public Switched Telephone Network ("PSTN") at data rates including 14,400 bps, 28,800 bps, 33,600 bps, 56,000 bps and others that are much slower than the about 10 Mbps to 30+ Mbps available on a coxial cable or HFC cable system on a cable television network.
With the explosive growth of the Internet, many customers have desired to use the larger bandwidth of a cable television network to connect to the Internet and other computer networks. Cable modems, such as those provided by 3Com Corporation of Santa Clara, Calif., U.S. Robotics Corporation of Skokie, Ill., and others offer customers higher-speed connectivity to the Internet, an intranet, Local Area Networks ("LANs") and other computer networks via cable television networks. These cable modems currently support a data connection to the Internet and other computer networks via a cable television network with a "downstream" data rate of 30+ Mbps, which is a much larger data rate than can be supported by serial telephone line used over a modem.
However, most cable television networks provide only uni-directional cable systems, supporting only a "downstream" data path. A downstream data path is the flow of data from a cable system "headend" to a customer. A cable system headend is a central location in the cable television network that is responsible for sending cable signals in the downstream direction. A return data path via a telephone network, such as a Public Switched Telephone Network provided by AT&T and others, (i.e., "telephony return") is typically used for an "upstream" data path. An upstream data path is the flow of data from the customer back to the cable system headend. A cable television system with an upstream connection to a telephony network is called a "data-over-cable system with telephony return."
An exemplary data-over-cable system with telephony return includes a cable modem termination system, a cable television network, a public switched telephone network, a telephony remote access concentrator, a cable modem, customer premise equipment (e.g., a customer computer) and a data network (e.g., the Internet). The cable modem termination system and the telephony remote access concentrator together are called a "telephony return termination system."
The cable modem termination system receives data packets from the data network and transmits them downstream via the cable television network to a cable modem attached to the customer premise equipment. The customer premise equipment sends responses data packets to the cable modem, which sends response data packets upstream via the public switched telephone network to the telephony remote access concentrator, which sends the response data packets back to the appropriate host on the data network. The data-over-cable system with telephony return provides transparent Internet Protocol ("IP") data traffic between customer premise equipment, a cable modem and the data network (e.g., the Internet or an intranet). As is known in the art, IP is a routing protocol designed to route traffic within a network or between networks.
When a cable modem used in the data-over-cable system with telephony return is initialized, it will make a connection to both the cable modem termination system via the cable network and to the telephony remote access concentrator via the public switched telephone network. If the cable modem is using telephony return, it will acquire telephony connection parameters on a downstream connection from the cable modem termination system and establish a Point-to-Point Protocol ("PPP") connection to connect an upstream channel to the telephony remote access concentrator. As is known in the art, PPP is used to encapsulate datagrams over a serial communications link. After a PPP connection is established, the cable modem negotiates a telephony IP address with the telephony remote access concentrator. The telephony IP address allows the customer premise equipment to send IP data packets upstream to the telephony remote access concentrator via the public switched telephone network to the data network.
The cable modem also makes an IP connection to the cable modem termination system so that IP data received on the cable modem termination system from the data network can be forwarded downstream to the customer premise equipment via the cable network and the cable modem.
Once an IP address is obtained on the cable modem termination system, the cable modem obtains the name of a configuration file used to complete initialization. The cable modem downloads a configuration file from a central location in the data-over-cable system using a Trivial File Transfer Protocol ("TFTP") server. As is known in the art, TFTP is a very simple protocol used to transfer files, where any error during file transfer typically causes a termination of the file transfer.
There are several problems associated with using a configuration file from a central location to configure a cable modem. In a typical cable modem initialization scenario, a Dynamic Host Configuration Protocol ("DHCP") is used to obtain an IP address and to obtain the name of a configuration file on a DHCP server from which configuration parameters are obtained for cable modem initialization. The configuration file is downloaded to the cable modem with TFTP using a TFTP server. Each DHCP server has an identical copy of the same configuration file. Thus, each cable modem in the data-over-cable system is configured exactly the same way with the same configuration file with TFTP.
Since all cable modems in the data-over-cable are not made by the same manufacturer and may be used for a number of different purposes, a single common configuration file is inappropriate for all cable modems in the data-over-cable system. However, if more than one configuration file name is used in a data-over-cable system, DHCP servers would be required to maintain a listing of configuration files for multiple cable modem types. This would not be practical in a data-over-cable system. In addition, modifying DHCP servers to use more than one configuration file violates the spirit of the DHCP standard and is expensive since a large number of DHCP servers, including third-party DHCP servers in the data-over-cable system would require modifications.
It is desirable to allow an individual cable modem to use configuration information from a configuration file different from the default configuration file without modifying existing DHCP servers or the DHCP initialization process used to obtain an IP address and a configuration file name.